Presentation on theme: "Design Issues for General-Purpose Adaptive Hypermedia Systems Hongjing Wu, Erik de Kort, Paul De Bra Eindhoven University of Technology The Netherlands."— Presentation transcript:
Design Issues for General-Purpose Adaptive Hypermedia Systems Hongjing Wu, Erik de Kort, Paul De Bra Eindhoven University of Technology The Netherlands
Topics AHAM Adaptation Engine AHAM-CA rule language for AHS Termination and confluence Static analysis in AHS Conclusions and future work
AHAM Run-time Layer Presentation Specification Adaptation Model Domain Model User Model Anchoring Within-Component Layer Storage Layer
Adaptation Engine (AE) Functions of AE –Offers generic page selectors and constructors –Provides a language –Performs adaptation –Updates the user model Features of well-behaved AE –Takes care of domain independent aspects –Provides timely response –Provides deterministic response
AHAM-CA Rules An AHAM-CA rule is defined as C A where: C states the rule’s condition as expression in “database- like” language A states the rule’s action as a database update. C: select P.access where P.access = true A: update F.pres := “show” where part-of(F,P) and F.relevant = true
Rule Instantiation 1.Instantiate all generic rules (use domain model) 2.For each specific rule Remove an instance of a generic rule if this specific rule with logically equivalent condition, and an action that updates the same attributes of the same concepts 3.Finally merge syntactically equivalent rules.
Rule Execution Semantics Rule C A is active when C new – C old Ø Repeat until no active rules remain: –Select an active rule –Execute the rule.
Rules Influence Each Other R i may activate R j If the execution of action A i may add elements to C j new, C j new – C j old Ø. R i may deactivate R j If the execution of action A i may remove elements from C j new, C j new – C j old = Ø.
Analysis Tools in Active Databases Activation (Deactivation) Graph –Nodes represents rules –Edge indicates one rule may activate (deactivate) another rule. Propagation Algorithm (PA) –R i may activate R j –R i may deactivate R j
Static Analysis of CA-rules Termination A rule set terminates if there are no cycles in AG. Confluence A rule set is confluent if all pairs of rules commute. –Two rules R i and R j commute if: (1)R i cannot activate R j (2)R i cannot deactivate R j (3)condition (1) and (2) with i and j reversed (4)R i ’s action and R j ’s action commute.
Static Analysis in AHS Less conservative then active databases –Only have updates to the user model (no insertions or deletions) –Use instantiated rules in analysis –Execution phases Improve Propagaition Algorithm –Properties from the value domain –C i is satisfied when A i is executed –Check AG (DG) for each possible event
Conclusions and Future Work Conclusions –Propose an abstract rule language AHAM-CA –Our analysis methods are less conservative than those in active databases Future work Create user-friendly authoring tools. Such authoring tools can offer support in the form of analysis tools.